The present invention relates to objects and their manufacture. More particularly, the invention is illustrated in an example using a novel combination of gases and a downstream plasma surface for selectively removing photoresist materials for substrates used in semiconductor integrated circuits. Merely by way of example, the invention can be applied in the manufacture of other substrates such as flat panel displays, micro electrical mechanical machines ("MEMS"), sensors, optical devices, and others.
In the manufacture of objects such as integrated circuits, processing safety and reliability have been quite important. Fabrication of integrated circuits generally require numerous processing steps such as etching, deposition, photolithography and others. In the photolithography process, for example, a photoresist film of material is often used to form patterns on thin slices of silicon or films that are deposited on such silicon. After patterning, however, it is necessary to remove the photoresist film from the silicon using a hydrogen bearing compound. Additionally, hydrogen bearing compounds are used in plasma treatment of silicon surfaces. In some cases, hydrogen is used to terminate ends of silicon bonds. Hydrogen is also used to remove oxides. Numerous studies have been made in using a hydrogen bearing compound, and in particular a low temperature process using a reductive reaction from atomic hydrogen produced by a hydrogen gas molecule gas plasma. For example, an object such as a wafer or hard disk has a surface, which is to be processed at a certain area or reactor exposed to high energy species such as ions even in the plasma downstream system. This way of processing occurs because lifetime of atomic hydrogen generated in the plasma is often short and can easily recombine into hydrogen molecules outside of the plasma discharge area. Thus, the conventional process often cannot avoid damage caused by high-energy species such as ions and electrons, decreasing the controllability of processing.
Numerous techniques using hydrogen for processing devices have been reported. As merely an example, a conventional process for ashing organic material, which is carbonized by ion implantation, using atomic hydrogen in a downstream plasma of hydrogen diluted by nitrogen or argon, has been reported by in a paper by S. Fujimura, H. Yano, J. Konno, T. Takada, and K. Inayoshi: Study on ashing process for removal of ion implanted resist layer, Process Symposium, Dry Process, Procedure Vol. 88-7, Honolulu, Hi., May, 1987 (The Electrochemical Society Inc. Pennington, 1988) pp. 126-133, which is incorporated herein by reference herein. It also has been reported that a high concentration atomic hydrogen is obtained in plasma downstream by the use of mixture of hydrogen and water vapor as the source gas for the plasma in J. Kikuchi, S. Fujimura, M. Suzuki, and H. Yano, Effects of H.sub.2 O on atomic hydrogen generation in hydrogen plasma, Jpn. J. Appl. Phys., 32, pp. 3120-3124 (1993) ("Kikuchi, et al."), which is incorporated by reference herein. Kikuchi et al. proposes a method to make an environment of a high concentration of atomic hydrogen at a downstream region where the influence of substantially all high energy species such as ions, electrons, and photons generated by plasma discharge can be substantially ignored.
Moreover, it was discovered that silicon native oxide could be eliminated at low temperature using NF.sub.3 injected downstream of a H2+H.sub.2 O plasma. This has been reported by J. Kikuchi, M. Iga, H. Ogawa, S. Fujimura, and H. Yano, Native oxide removal on Si surface by NF3-added hydrogen and water vapor plasma downstream treatment, Jpn. J. Appl. Phys., 33, 2207-2211 (1994). This silicon native oxide removal process with NF.sub.3 -added hydrogen and water vapor plasma downstream treatment achieved a removal of silicon native oxide at nearly room temperature in vacuum environment and formation of hydrogen terminated silicon surface. Thus, the reported process can replace the conventional high temperature hydrogen gas pre-treatment of silicon epitaxy. J. Kikuchi, M. Nagasaka, S. Fujimura, H. Yano, and Y. Horiike, "Cleaning of Silicon Surface by NF.sub.3 -Added Hydrogen and Water-Vapor Plasma Downstream Treatment," Jpn. J. Appl. Phys., 35, 1022-1026 (1996). Additionally, it was suggested to use this method for the several applications of a silicon based semiconductor-manufacturing process such as cleaning of a contact hole of ULSI devices, J. Kikuchi, M. Suzuki, K. Nagasaka, and S. Fujimura. The silicon native oxide removal with using NF.sub.3 -added hydrogen and water vapor plasma downstream treatment 4. Extended Abstracts (The 44th Spring Meeting, 1997); The Japan Society of Applied Physics and Related Societies, 1997, (29p-W6) in Japanese.).
The aforementioned technologies generally required introducing a high concentration of a hydrogen gas into a plasma. The high concentration of hydrogen causes an absolute risk of an explosion. Accordingly, a high-level safe system has to be prepared for practical use of this technology. For example, restrictions of the use of rotary vacuum pump with conventional vacuum pump oil should be prepared. A requirement of a vacuum load lock system in order to prevent the leaking of hydrogen from reaction reactor also need be prepared. A further requirement would include a high volume dilution inert gas system at exhaust pump gas in order to reduce the concentration of hydrogen lower than its explosion limit. Moreover, the system would also require a hydrogen gas leak-monitoring system, a fire extinguishing system, and an alarm system for the inside of equipment or installed room itself. These safety requirements will generally result in high costs to use this technology and it will become an obstacle to the growth of the technology in the industry.
From the above, it is seen that an improved technique of fabricating a substrate in an easy, cost effective, and efficient manner is often desirable.